Various types of veterinary insulins are known as PZI, "Protamine Zinc Insulin".
[1] The ones we use most often for animals are a combination pork/beef-derived insulin or a beef-derived insulin. Because most are veterinary insulins, PZIs are not available at normal human pharmacies.

PZI veterinary insulins are intermediate-acting to long-acting, and can be closer in molecular structure to a cat or dog's own insulin than human-type or analog insulins. PZI is rarely used in dogs but is considered when other insulins are not effective. [2][3][4] An R-DNA/GE/GM U 40 manufactured PZI, ProZinc, has just been approved in the US for use in cats; it has not been studied in dogs. [5]

PZI itself was introduced in 1936; it was the first insulin having any type of suspension[6]. But the combination of insulin and protamine produced by Novo Nordisk's Hagedorn and his colleagues was not stable and required patients to add a neutralizing liquid to the vial before it could be used. By 1938, Canadians D. A. Scott and A. M. Fisher discovered adding zinc to the mixture stabilized the insulin so that it only needed to be resuspended before being used. [7][8] Before PZI, the only insulin available was R/Neutral, having no additives to alter or extend its action. Until then, many with diabetes had to get up during the night to take an insulin injection because R/Neutral did not last long enough for an uninterrupted night's sleep. [9]

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According to the UK's National Health Service, [10] in cases where a shorter-acting insulin is needed in addition to the PZI, the protamine zinc insulin must always be injected separately--NO mixing--due to the excess of protamine in the insulin formula. [11][10][12][13]

These are manufactured, not compounded, insulins. This means the insulin keeps longer, and is less likely to vary, as compounded insulins can, from batch to batch. The manufactured insulins have a shelf life of three years (unopened).

All Insuvet insulins have been discontinued by Pfizer Animal Health.[22][23][24] The insulins were made under contract by Wockhardt UK for both Pfizer and for Schering-Plough Animal Health, who owned the brand name earlier. Wockhardt makes the same insulins under their Hypurin brand name.[25]

Schering-Plough Animal Health contracted CP Pharma to produce its Insuvet line of bovine insulins. [25] The Insuvet line was sold to Pfizer Animal Health and it is believed that Pfizer continued to contract CP/Wockhardt UK for their production.

CP Pharma is based in the UK and is now the only supplier of manufactured bovine PZI. In other countries, you can import insulin from them or, if you are in North America, the compounded PZI in various strengths available from BCP and VPOA (US) and Summit (Canada).

Those CP Pharma insulins are comparable to Insuvet Protamine Zinc, by Pfizer Animal Health, formerly by Schering-Plough Animal Health, a U100, 100% bovine PZI for veterinary use that is only available in the UK.

CP Pharma actually produced the Schering-Plough Animal Health Insuvet insulins. [25] After the Insuvet line was sold to Pfizer Animal Health, it's believed that Pfizer continued to contract CP/Wockhardt UK for their production.

Stokes compounding pharmacy in New Jersey is now offering compounded porcine (pork) PZI insulin.[33][34] Stokes offers its bovine (beef) PZI insulin in both U100 and U40 strengths; it's likely their pork PZI would also be available in both insulin strengths.[35]

Those in Canada can obtain 100% beef compounded PZI in U100 strength from Summit Veterinary Pharmacy [36] in Ontario. Summit sells their insulin solely through vets--yours will need to place the order for you.

There are also pharmacies in the US and UK that compound PZI based on human ("regular") or animal-source insulins. It is possible to have PZI Humulin insulin of any strength compounded at some local compounding pharmacies. [37]

This link [38] and this one [39] list some of those compounding pharmacies, their contact information, and prices for their insulins.

Your vet may also be able to obtain manufactured PZI insulin for you through Health Canada's Emergency Drug Release program. [40] With it, you are able to receive up to 6 months worth of insulin; a C$ 50.00 fee for the application is required. [41] If permitted, you would then be eligible to import PZI insulins such as Hypurin Bovine Protamine Zinc, as well as the other insulins CP Pharma produces.

The program is similar to Health Canada's Special Access Programme [42] for importing necessary drugs for people.

Some Rules for Dosage of Protamine Zinc Insulin Chase, Lillian A., 1938, Canadian Medical JournalThis dates back to 2 years after PZI was introduced. Though these are human experiences, it may provide some insight into using pure beef PZI. "Unmodified Insulin" referred to is today's R/Neutral type.